State Route 120 (SR 120) is a state highway in the U.S. state of California, running west to east across the central part of the state. It runs from the San Joaquin Valley near Lathrop through Yosemite National Park, to its end at U.S. Route 6 in Mono County, eastern California. While the route is signed as a contiguous route through Yosemite National Park, the portion in park boundaries is federally maintained, and is not included in the state route logs. The portion at Tioga Pass is the highest paved through road in the California State Route system. This part is not maintained in the winter and is usually closed during the winter season.

SR 120 begins as a freeway intersecting Interstate 5 to extend Interstate 205 through Manteca. In east Manteca the freeway ends at SR 99 and becomes a highway which continues to head east through Escalon, Oakdale and other various small towns. East of Oakdale there are no highly populated areas for 90 miles (144 km) as it heads into the foothills of the Sierra Nevada and into Yosemite National Park. Entering Yosemite, SR 120 is known as Big Oak Flat Road as it heads towards Crane Flat. After leaving Crane Flat, Big Oak Flat Road turns southeast towards Yosemite Valley, while SR 120 continues east as Tioga Pass Road (or often simply Tioga Road).[2] The highway retains that name as it travels through Tuolumne Meadows, over Tioga Pass at an elevation of 9,945 feet, and through the Lee Vining Canyon on its 59-mile (95 km) journey to its intersection with U.S. Route 395, at Lee Vining. After a jog to the south along US 395, it continues east as Mono Mills Road,[3] skirting the south end of Mono Lake and providing access to the Mono Lake South Tufa as well as the historical site of Mono Mills before cresting Sagehen Summit and ending with the intersection of U.S. Route 6 at Benton. Both the portions through Yosemite National Park and the stretch south of Mono Lake are subject to winter closure. Usually the highway is open through Tioga Pass by the Memorial Day weekend at the end of May, and typically closes for the winter sometime in November.

Tioga Road/Big Oak Flat Road is officially both a National Scenic Byway and a National Forest Scenic Byway.[4] The segment through the Lee Vining Canyon between the eastern edge of Yosemite and US 395 is designated as the Lee Vining Canyon Scenic Byway, a separate National Forest Scenic Byway.[5]

During the Gold Rush, SR 120 was originally known as Big Oak Flat Road, after the village of Big Oak Flat through which it passes in the Sierra foothills. It was a pack trail from Stockton which became popular with prospectors about 1849. By 1874 it was a wagon road which extended to Yosemite Valley.

West of Priest is a section of highway with over one hundred curves and hairpin turns, known as the "New Priest Grade." With a 4% grade, it opened in 1915 and was built by a group of local volunteers who desired an alternative to the very steep (17%) Old Priest Grade.[17] Today, both grades are paved, but trailers and RVs are prohibited from Old Priest Grade.[18] There is a 7,500-pound weight limit on the old grade.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see the list of postmile definitions).[1] Segments that remain unconstructed or have been relinquished to local control may be omitted. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.